Photovoltaic system that covers its monthly costs by itself and amortizes

The lifespan of a system is often given as 20-25 years. Is that really the case? Do individual cells or modules then break, or will a complete replacement be necessary later?

I exported the daily values (production, consumption, self-consumption, feed-in) via SE. That results in a pretty long Excel list. Here, I then (simplified) ran a query: "How much consumption could I have covered with a storage capacity of 6 kWh on day x (1...365) instead of the feed-in." It is taken into account in a blanket manner beforehand that the available capacity is about 90% and the charging/storage losses in relation to the feed-in (!) are about 20% (realistic according to various storage studies, with charging forecasts and other improvement methods you might get it down to 10%, but that’s already very optimistic). But even if it were 0, that would only slightly affect the calculation.

Well, simplified it looks like this, for example: Very good day: 07/27: 54 kWh yield; 47.2 kWh feed-in; 12.2 kWh consumption; 6.8 kWh direct consumption; 4.8 kWh possible battery consumption Unfavorable day: 10/05: 3.5 kWh yield; 0.6 kWh feed-in; 15.4 kWh consumption; 2.9 kWh direct consumption; 0.2 kWh possible battery consumption Summed up, you get what I can store in a year, for me 1000 kWh. On most days that’s about 1.5-3 kWh. The 200 I subtract are the losses from storing, charging, grid consumption, etc.

Not considered are what makes it even less favorable for the battery: - Storage charging also takes place during the morning forecast and around midday, but there are many days when the sun shines more in the afternoon or in the morning mainly direct consumption occurs - The battery inevitably draws power from the grid if there is not a bright blue sky all day

but that’s why the 80% losses are there… they roughly cover that.